Ever since the oil crisis, efforts have been undertaken for seeking other energy sources. One proposed energy source is to convert the kinetic energy of running water in an ocean, sea or river into usable form. However, most of the conventional hydraulic engines designed for this purpose utilized the energy of water flowing through the engine itself. The present inventor has taken into consideration the possibility of utilizing the whole kinetic energy of flowing water in a fixed length of pipe. The impulse produced by the water is first abosrbed through a complex piston means containing a compressible elastic substance and later released to actuate a crankshaft of the engine. The installation and maintenance cost of the engine is reduced due to the simplicity of the engine and mechanical efficiency is increased.